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Date:      Sun, 30 Dec 2018 23:18:14 +0100
From:      =?UTF-8?B?VMSzbA==?= Coosemans <tijl@FreeBSD.org>
To:        Andrea Venturoli <ml@netfence.it>
Cc:        freebsd-x11@freebsd.org
Subject:   Re: Radeon HD 4250: screen going blank every few seconds
Message-ID:  <20181230231814.4bf4cbff@kalimero.tijl.coosemans.org>
In-Reply-To: <20181230224607.1feb9cad@kalimero.tijl.coosemans.org>
References:  <4560f9e2-efcf-a1f5-728c-c26fcec34353@netfence.it> <20181230224607.1feb9cad@kalimero.tijl.coosemans.org>

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On Sun, 30 Dec 2018 22:46:07 +0100 T=C4=B3l Coosemans <tijl@FreeBSD.org> wr=
ote:
> On Sun, 30 Dec 2018 20:29:49 +0100 Andrea Venturoli <ml@netfence.it> wrot=
e:
>> I've got a desktop which used a Radeon HD 4200 with no troubles: I was=20
>> using a 1920x1200 monitor on the DVI port and occasionally a second one=
=20
>> on the VGA port; this system had no HDMI port.
>>=20
>>=20
>>=20
>> Now I changed mainboard with an Asus M5A88-V Evo (latest BIOS=20
>> installed), which features a Radeon HD 4250 and I'm getting some trouble=
s.
>>=20
>> Focusing only on one monitor, it works fine if connected to the VGA=20
>> port, but I'd like to avoid this setup because:
>> a) begin analogic, it shows some background noise;
>> b) it won't allow me to use the second monitor.
>>=20
>> So I'd like to use either the HDMI or the DVI port, but in this case:
>> _ the system start fine and is stable as long as BIOS resolution is used;
>> _ as soon as I "service kld start" and the resolution switchs to=20
>> 1920x1200 the screen starts flickering: every 1-2 seconds the image goes=
=20
>> black (the monitor displaying "DVI Input" or "HDMI Input" as if a new=20
>> signal was detected) and gets back to normal in another 1-2 seconds;
>> _ once XOrg is up and running the problem does NOT disappear.
>>=20
>> As I suspected an hardware problem, I tried booting Knoppix: initially I=
=20
>> get the same behaviour (works fine, then starts flickering once the=20
>> resolution is increased); however, after XOrg is running the problem sto=
ps.
>> So, either it isn't an hardware problem or there is a workaround.
>>=20
>> Also worth mentioning:
>> _ if I decrease the resolution to 1920x1080 everything is ok, of course=
=20
>> apart seeing two black areas on the top and bottom of my screen :(
>> _ while keeping full resolution, attaching the second monitor on the VGA=
=20
>> port *and enabling it* will reduce the flickering from every 1-2 seconds=
=20
>> to every 5-10 seconds.
>>=20
>>=20
>>=20
>>=20
>> So I'm asking for some help, since either using the VGA port or=20
>> decreasing the resolution is not a workaround I'm eager to adopt; is=20
>> there anything that can be done? Some sysctl? Some BIOS settings? Some=20
>> xorg.conf tweak? Some update to test?
>>=20
>> I tried and searched if this was a known (or at least previously seen)=20
>> problem, but came up empty.
>> Even some pointer to documentation/knowledge base would help... =20
>=20
> Try running "sysctl compat.linuxkpi.hw_i2c=3D0".

This seems to be a loader tunable so you'll have to add
compat.linuxkpi.hw_i2c=3D0 to /boot/loader.conf and reboot.



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